Autocad 2014 Ita Torrent
Kody Coste
While not open souce BricsCAD IS a drop in replacement for Autocad. It even uses most of Autocad's same commands. It is also about 1/2 to 1/3 the price. BricsCAd also has a large community using the product. As a 20 autocad user, it only took minutes for me to get up and running with BricsCAD.
Basic version of Draftsight is free for anyone, and there is a Linux version. You have to register but they don't hassle. The CAD engine is from Graebert who produce ARES Commander, and the same is in CorelCAD.
I need to produce industry standard 2D CAD drawings and Draftsight is the only product I have found that will allow this on Linux. (Yep, 2D is certainly not obsolete - millions of us still have to produce 2D stuff.)
Otherwise, FreeCAD looks interesting, but is only at about version 0.16 so it has a way to go. There are already autocad dwg import functions, Hopefully someone will do some AutoCAD command aliases for FreeCAD. Who knows - maybe I'll end up doing them :-)